This research provides an advanced understanding of the physiological responses of two algal species, Chlorella vulgaris and Scenedesmus subspicatus (Chlorophyta) to changing environmental conditions likely to occur in Waste Stabilisation Ponds (WSPs). Bicarbonate was found to be a suitable carbon source for both species. Maximum growth rates of around 0.07 h⁻¹ were achieved at concentrations of around 10 mmol C 1⁻¹. The results showed that nitrate uptake became increasingly light dependent with increases in temperature. Phosphate was taken up from the medium in excess of immediate growth requirements and uptake rates did not show light or temperature dependence at the range of concentrations used. Respiration rates were shown to depend on light and temperature. Photosynthetic activity was registered at light intensities as low as 7.8 µmol m⁻²s⁻¹ and 5°C of temperature. Both light and temperature affected growth rates. Both species reached maximum light-specific growth rates at 47.0 µmol m⁻²s⁻¹ at all temperatures tested. Below 15°C C. vulgaris showed higher growth rates than S. subspicatus, but this was reversed at 20°C. Experiments on survival showed that a proportion of cells of C. vulgaris could survive long periods (22 weeks) of dormancy in complete darkness and low temperatures (+4 and -20°C). Despite a hardening procedure, S.subspicatus showed no survival after exposure to -20°C and limited ability to resume growth and carry out photosynthetic oxygen production after exposure to +4°C and complete darkness up to 14-15 weeks. Overall the results indicate that C. vulgaris is better adapted to growth at low temperature and light intensities, but may be out-competed by S. subspicatus in warmer brighter conditions.